Airbag and method of producing an airbag

ABSTRACT

The invention relates to a two-ply airbag consisting of a textile surface structure, said plies lying opposite one another and enclosing at least one chamber that can be filled with gas. The piles have surfaces that face outwards. The airbag is characterized in that coatings, which are suitable for sealing and reinforcing the airbag, are applied to said surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT Application No. PCT/EP03/05697filed on May 30, 2003, which claims priority to German Application No.DE 102 24 771.4-42, filed on Jun. 4, 2002; both of which areincorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an air bag comprising two plies of a textilesheet fabric, the plies facing each other and enclosing at least onechamber that can be filled with gas, the plies having surfaces facingoutwards, the invention also relating to a method of producing such anair bag.

Air bag fabrics are in use whose technical properties are dictated bythe dense structure of the fabric. To attain the needed strength andairtightness the fabric must be fabricated suitably high set whichbecause of the high material consumption results in fabrication beingexpensive. Fully fabricated or one-piece woven (OPW) air bags need tosatisfy the crash withstanding performance, in other words it is vitalthat the pressure in the air bag is maintained for the criticalduration, i.e. the air bags must not leak. For this purpose such airbags are woven extremely dense, major efforts being made to change theweave in the transition of two-ply portions into single-ply portions inattaining, for example, a high fabric tear strength or comb withdrawalforce.

Since in many cases the air bag fabric made in this way still fails toexhibit an adequate leakage resistance, additional thin films are addedin an expensive process with the sole objective of sealing the finepores of the fabric to achieve the necessary leakage resistance. Airbags fabricated as such are, on the one hand, because of the weavingmethod very expensive. On the other, the expense of the air bags isfurther increased by the complicated coating process. Because of itshigh density, finishing such a fabric is a slow and thus cost-intensiveprocess.

Known air bag fabrics have the further drawback that because of thedense set and involving the slower weaving process the load on the yarnis correspondingly higher. Thus, during the transition in weaving thethreads from the upper into the lower position and vice-versa thethreads rub against each other all the more often and intensifiedbecause of the dense set, to the detriment of the quality in weaving(capillary damage, fluffing, conglomerations, thread breakage and thelike) resulting in a high degree of spoilage. Moreover, thread damage inweaving results in many cases in downtime of the weaving machine, alsodue to machine speeds needing to be increasingly higher causing aserious loss of efficiency which in turn further adds to the alreadyhigh costs of production. Another drawback of the air bags as discussedis that due to the high set and because of the correspondingly highfabric thickness of the air bag fabric a certain packing volume of thefinished air bag needs to be assured in the folded condition. Because ofthe high set the fabric or air bag becomes stiffer, further adverselyinfluencing working the fabric.

The present invention is based on the objective of producing a low-costair bag in avoiding or at least greatly diminishing the drawbacks ofprior art, as well as proposing a method for producing such an air bag.This objective is firstly achieved by an air bag as it reads from claim1. This air bag in accordance with the invention can now be fabricatedsignificantly cheaper than air bags as known from prior art. Byarranging the coatings on the surfaces of the fabric plies of the airbag facing outwards as suitable for forming the leakage resistance andstrengthening of the air bag, the textile sheet fabric of the air bagcan now be woven relatively loosely. Strengthening the air bag in thissense is meant as coating the air bag to achieve particularly highstrength, leakage resistance and keying to the fabric. The fabric itselfis responsible so-to-speak for forming the outer and inner structure ofthe air bag and its at least one chamber, i.e. it not primarilycontributing towards leakage resistance and strength of the fabric ashandled namely by the coating e.g. also in the form of a film. Now,because of this, the set of the fabric can be strongly redimensioned.Thus, for instance, the single-ply portions in a one-piece woven (OPW)can now be executed solid and tight in a (simpler) plain weave insteadof a panama weave as hitherto. This greatly reduces the load on thefabric by shear forces at critical transitions from single-ply totwo-ply portions with the same weave as achieved by the plain weave asproposed in this case, resulting in a drastic reduction in the risk ofthe coating becoming detached or damaged as arranged on the fabric, i.e.risk of leakage. By satisfying the required airtightness the air bag inaccordance with the invention thus ensures the vital pressurewithstanding duration.

Another advantage materializes from the smoother surface of the plainweave permitting better adhesion of the coating in further reducing therisk of leakage. Because of the lower set and the resulting higheroutput of the weaving machine, the air bag fabric and one-piece wovens(OPW) in the shop and finishing can now be produced and worked toadvantage substantially cheaper. Due to the fewer shed changes as wellas due to the lesser attrition of the threads against each other theload on the yarn material is significantly reduced, resulting in adrastic reduction in impairments (capillary damage, fluffing,conglomerations, thread breakage and the like) in thus immenselyenhancing product quality. Since this involves the weaving machine beingdown far less because of yarn impairment, efficiency is boostedsubstantially.

Yet another advantage of the air bag in accordance with the inventionmaterializes from the reduced packing volume in the folded condition.The reduction in set as made possible by the invention now makes itpossible to reduce the cover factor and result in a fabric with a softerfeel with added flexibility. As a result of this, the fabric coming fromthe weaving machine can now be worked much better in the subsequentsteps in the process. Further features and advantages of the inventionread from the sub-claims.

The objective is further achieved by a method as it reads from claim 8.For this purpose, particular mention is made to the advantages of hotrolling thermoplastic films to the surfaces, resulting in the keyingpoints in the fabric being flattened by the pressure in thus providing amore expansive receiving surface for the roll-applied films. In otherwords, this relatively simple trick now makes it possible to achieve asmoother surface for better keying between coating and fabric. As a rulethe surfaces of e.g. of woven, knitted or netted textile sheet fabricsas representing the aforementioned surfaces, for example, are not smoothin structure but “bumpy”, resulting in no continuous flat contactsurface being available for a coating, e.g. in the form of a film. Thethreads of the textile sheet fabric merely “ripple” from the surfacethereof in a bumpy structure, whereby in a knit, for example, the peaksof the loops protrude from the surface whilst the valleys of the loopsare located deeper in the knit.

It is known to coat textile sheet fabrics with fluids, films, film-likematerials or laminates and the like, serving e.g. to enhance theresistance to ageing and/or leakage and/or to reduce permeability and/orfriction, etc. When such textile sheet fabrics are overtaxedmechanically, hydraulically or pneumatically the key between the textilesheet fabric and the coating is disrupted which may even result in atotal malfunction of the textile sheet fabric.

In another advantageous aspect of the method in accordance with theinvention as it reads from claim 9, a low-cost method of coating textilesheet fabrics, especially where wovens, air bag wovens and air bags areinvolved in achieving a better adhesion between the textile sheetfabrics and their coatings. A substantial improvement in the adhesion ofthe textile sheet fabric is achieved both by corona treatment and byplasma treatment as well as by fluorination. In the corona and plasmaprocesses as described and discussed e.g. in German utility model DE 29805 999 U1 electrostatic forces of attraction are activated to greatlyenhance the adhesion of the substances applied to the textile sheetfabric. In fluorination of a textile sheet fabric, a reproducible, drychemical reaction takes place at the surface in which hydrogen atoms aresubstituted by fluorine, creating a longer-active surface permittingmechanical and chemical bonding.

In still another advantageous aspect of the method in accordance withthe invention the textile sheet fabric is coated with a film of siliconewhose surface facing away from the textile sheet fabric is treated withfluorine gas. This fluorination produces a near totally smooth surfacepractically cancelling any silicone/silicone adhesion. This advantage isput to use particularly for air bags to be folded, since it does awaywith the need for a parting agent as required hitherto.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be briefly explained in the following by way ofan example embodiment with reference to the drawing in which:

FIG. 1 is a diagrammatic cross-section through a fabric ply of an airbag in accordance with the invention.

FIG. 2 is a diagrammatic illustration of how thermoplastic films arerolled on to a fabric ply for producing a textile sheet fabric for theair bag in accordance with the invention.

DETAILED DESCRIPTION

Referring now to FIG. 1 there is illustrated a fabric including weftthreads 6 and (not shown true to scale) warp threads 7. Indicated areso-called keying points 2 to which a film 1 optimized as to adhesion,resistance to leakage and strength is applied to a fabric 3 formed byweft and warp threads 6 and 7 respectively. Due to the fabric 3 beingcompressed by a pair of nip rollers 4 as shown in FIG. 2 the warpthreads 7 are squeezed together so that they become ellipticalcross-sectionally. Likewise evident from the arrangement as shown inFIG. 1 simply diagrammatical is how the keying “points” 2 becomeflattened between film/coating and fabric.

Referring now to FIG. 2 there is illustrated a pair of nip rollers 4between which the film 1 as cited above and the backing fabric 3 thinnedin the thread densities is guided and keyed. The resulting key offilm/coating and fabric is achievable, chemically, thermally ormechanically, resulting in so-to-speak a textile-strengthened plasticssurface 5 which can be additionally compounded by making use ofbicomponent yarns. In a loose fabric setting the ondulation of thefabric is less. The keying points 2 of the textile-strengthened plasticssurface 5 are flattened by the pressure in rolling and offer a largercontact surface for the film 1.

The air bag may also be configured as it reads from claim 3, whereby theadvantages as discussed with reference to claim 1 are likewise provided.By thermally treating the air bag after weaving the necessary leakageresistance and strength are attainable due to cross-linking of thecomponents of the plastics sheathing the threads of the fabric plies.

1. An air bag comprising two non-gastight plies of a textile sheetfabric, the plies facing each other and enclosing at least one chamberthat can be filled with gas, the plies having surfaces facing outwards,comprising a fabric dictating the outer and inner structure of the airbag and on each surface facing outwards one coating is disposed forstrengthening and rendering the air bag resistant to leakage.
 2. The airbag as set forth in claim 1, wherein said coatings comprise films keyedto the surfaces chemically, thermally or mechanically.
 3. The air bag asset forth in claim 1, wherein the coatings comprise plastics-sheathedthreads of the fabric plies.
 4. The air bag as set forth in claim 1,wherein said textile sheet fabric is a woven.
 5. The air bag as setforth in claim 1, wherein said textile sheet fabric is a knit or anon-woven fleece.
 6. The air bag as set forth in claim 4, wherein saidtextile sheet fabric comprises bicomponent yarns.
 7. The air bag as setforth in claim 1, wherein said textile sheet fabric is a thinned fabric,whose surface is laminated with a coating or film.
 8. A method ofproducing an air bag comprising two woven plies facing each other andenclosing at least one chamber that can be filled with gas, the plieshaving surfaces facing outwards, on which coatings, laminates, films orcovering layers are deposited suitable for strengthening and/orrendering the air bag resistant to leakage, comprising the steps:weaving the air bag on a weaving machine controlled particularly by aJacquard device, hot rolling thermoplastics films on the surfaces, thekeying points in the fabric being flattened by pressure in thus forminga larger contact surface for the films.
 9. The method as set forth inclaim 8, wherein said surfaces and/or coatings, laminates, films orcovering layers are prepared at least in part by a corona treatment orby a plasma treatment or by fluorination before roll application of thefilms.
 10. The method as set forth in claim 8, wherein films ofpolyamide, polyester, silicone, neoprene or polyurethane are laminatedto said surfaces.
 11. The method as set forth in claim 8, wherein saidsurfaces are provided with a film of silicone which is in turn treatedwith fluorine gas.